Apparatus for controlled cooling of metal samples

ABSTRACT

THIS PATENT DISCLOSES A METHOD AND APPARATUS FOR CONTROLLED COOLING OF METAL SAMPLES, E.G., SPECIMENS REPRESENTING INTERIOR PORTINS OF STEEL PLATES HAVING A THICKNESS OF ABOUT 2 TO 10 INCHES. THE PRACTICES USED PRIOR TO THE INSTNAT INVENTION FOR SIMULATING THE COOLING OF SUCH PARTS OF SUCH STEEL PLATES FROM AN AUSTENITIZING TEMPERATURE IN THE HEAT TREATMENT THEREOF ARE QUITE CUMBERSOME AND LABORIOUS, INVLOVING SEVERAL TRANSFERS OF THE SPECIMEN FROM ONE FURNACE OR MEDIUM TO ANOTHER, AND AT THAT, THE SIMULATION OBTAINED IS RATHER INEXACT AND UNRELIABLE. THIS PATENT DISCLOSES TAHT A BETTER SIMULATIN IS OBTAINED, WITH FAR LESS LABOR AND THE USE OF FAR LESS EQIUPMENT, BY CONDUCTING THE COOLING OF THE SAMPLE IN A FLUIDIZED BED OF SILICA SAND OR THE LIKE, USING GASEOUS PRODUCTS OF COMBUSTION OR OTHER SUITABLE GAS AS THE FLUIDIZING MEDIUM. SLOW RATES OF COOLING MAY BE SIMULATED BY CONTROLLING THE TEMPERATURE OF THE FLUIDIZING GAS, AND/OR THE TEMPERATURE OF THE FURNACE SURROUNDING THE FLUIDIZED BED. FASTER RATES OF COOLING ARE SIMULATED BY ADDING SOLIDS TO THE BED AT A CONTROLLED RATE.

United States Patent [72] inventor Jerome Feinman 1335 Woodland Drive, Monroeville, Pa. 15146 [21] Appl. No. 663,349 [22] Filed Aug. 25, 1967 [45] Patented June 28, 1971 [54] APPARATUS FOR CONTROLLED COOLING 0F METAL SAMPLES 1 Claim, 3 Drawing Figs.

[52] [1.8. (l 266/5 [51] lnt.Cl. C2lcl/44 [50] Field of Search 266/4, 4 4 (F), 5. 5 (E), 5 (F), 5 (T), 6; 148/13.1; 263/41 [56] References Cited UNITED STATES PATENTS 2,118,642 5/1938 Flynn et al. (266/5T) 2,835,483 5/1958 Lindsay (266/5) 3,197,328 7/1965 Jung et a1... 266/5(X) 3,197,346 7/1965 Munday 148/l3.1(X) 3,355,159 11/1967 Ayers 266/5(X) FOREIGN PATENTS 537,501 5/1955 Belgium 266/4 Primary Examiner-J. Spencer Overholser Assistant Examiner-R. Spencer Annear Attorney-John W. Linkhauer ABSTRACT: This patent discloses a method and apparatus for controlled cooling of metal samples, e.g., specimens representing interior portions of steel plates having a thickness of about 2 to 10 inches. The practices used prior to the instant invention for simulating the cooling of such parts of such steel plates from an austenitizing temperature in the heat treatment thereof are quite cumbersome and laborious, involving several transfers of the specimen from one furnace or medium to another, and at that, the simulation obtained is rather inexact and unreliable. This patent discloses that a better simulation is obtained, with far less labor and the use of far less equipment, by conducting the cooling of the sample in a fluidized bed of silica sand or the like, using gaseous products of combustion or other suitable gas, as the fluidizing medium. Slow rates of cooling may be simulated by controlling the temperature of the fluidizing gas and/or the temperature of the furnace surrounding the fluidized bed. Faster rates of cooling are simulated by adding solids to the bed at a controlled rate.

PAIENTED JUN28 lsn Curve Follow/0g Control/er INVENTOR. JEROME FEINMAN y WW Attorneys APPARATUS FOR CONTROLLED COOLING F METAL SAMPLES BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to the heat treatment of metals, and in particular, to a method and apparatus for the controlled cooling of metal samples, such as specimens representing the central portions of metal plates.

2. Description of the Prior Art In the heat treatment of steel plates, such as boiler plates about 2 to inches thick, it has periodically proved desirable to learn the effect upon the properties of the metal in the interior portions of the plate of a heat treatment that involves cooling from a suitable austenitizing temperature, such as about 1,600 F. In the heat treatment of such plates, cooling rates more or less rapid are obtained, depending upon the thickness of the plate, the diffusivity of the material of which it is composed, and the nature and temperature of the cooling or quenching medium. For some purposes, it has proved necessary to take a full-sized plate, subject it to an experimental heat treatment, and remove and test a corner portion thereof, with the result that a portion of the plate across its width and as long as the height of the corner portion removed must be scrapped; this makes such testing very expensive. Productionscale heat-treating facilities are used, and a large piece of steel is scrapped.

In accordance with another practice for obtaining an indication of the effect of a particular experimental heat treatment upon the properties of the material at the center of a sample of steel subjected to that experimental heat treatment, there are used specimens substantially thinner than the plate and of considerably smaller dimensions. Such specimens are heated to the austenitizing temperature, and then outfitted with thermocouples and moved from one furnace or bath of molten material to another, with the separate furnaces or baths being maintained at a particular temperature. Much equipment is required and considerable careful attention from the operator. At best, a simulation obtained in this manner is rather inexact, and it is almost impractical to obtain in this way a satisfactory simulation of a cooling that proceeds very slowly, such as over a period of about 2 days or longer.

It must also be admitted that certain parts of the equipment used in the apparatus of the present invention, and certain steps used in the method of the present invention, are themselves old. For example, the technique of using a fluidized bed of finely divided solids is well known, having been used in such applications as the application of a coating of finely divided polyethylene to a heated metal substrate, the reduction of iron ore to sponge iron with hydrogen gas, and the burning ofi of carbonaceous contaminant from nickeliferous hydrogenation catalyst. So far as I am aware, however, the idea of controlling the overall heat capacity of such a fluidized bed in such a way as to cause the temperature of a steel sample contained therein to follow a predetermined program, by introducing cool solids into the bed and simultaneously withdrawing mixed bed solids, is new.

In accordance with the present invention, a bed of silica sand or the like is heated with combustion gases, the temperature of which may be varied by supplying different amounts of excess air to the combustion. It is known, for example, from Bulletin No. 44,23, Jan. 1963, published by the North American Manufacturing Company, Cleveland, Ohio, to provide a burner capable of using such different amounts of excess air.

A further aspect of the present invention involves the provision of solids to the fluidized bed at different volumetric rates of flow, and equipment for achieving this objective is part of the prior art. See, for example, the catalog No. 320,200 of Wallace & Tiernan, lnc., Bellevillc, New Jersey, published 1964, showing a Series C belt-type volumetric feeder. This equipment is capable of achieving various volumetric rates of flow ranging from 4 pounds per hour to 400 pounds per hour,

in accordance with electrical command signals supplied to a control unit contained therein.

It is also known to use a controller-recorder of a kind having a strip chart, upon which there is traced with a silver pencil a line indicative of the changes, in a given period of time, in a desired value of a certain parameter, the controller having means for generating a signal in accordance with the line traced, means for sensing the actual value of the parameter being controlled and producing a signal corresponding thereto, and means for comparing the two signals and generating an appropriate command signal or error signal that may be fed to equipment capable of effecting an appropriate adjustment in the parameter being controlled. Such a controllerrecorder is called a curve-following strip-chart recorder.

SUMMARY OF THE INVENTION In accordance with the invention, metal samples are subjected to a controlled cooling from an austenitizing temperature by being placed in a bed of silica sand or the like fluidized with gases resulting from a combustion taking place in a plenum chamber immediately below the bed. The bed is surrounded with insulation and/or heating means, and is provided with an overflow standpipe and, if desired, sample-holding means. The apparatus of the invention further comprises means for feeding solids to the bed; ordinarily, the solids are at about room temperature, and preferably, the solids-feeding means is of a type that may be set or controlled to deliver solids at gravimetric or volumetric feed rates within a particular range. By appropriate adjustment of the power supply to the heating element surrounding the furnace and/or the rate at which solids are fed to the bed, samples or specimens of metal may be conveniently subjected to a cooling treatment of desired time-temperature characteristics, e.g., a treatment designed to simulate the time-temperature history of metal in the interior of a plate about 2 to 10 inches thick when quenched from an austenitizing temperature in a particular medium. Though the equipment mentioned above is all that is required for practicing the invention in its broadest aspects, it is preferred that there also be provided strip-chart-controlled means of the kind described above, receiving temperature signals from the sample immersed in the bed and controlling the heating means and/or the solids-feeding means so as to keep the temperature of the specimen or sample in the bed at a value indicated by the trace on the strip chart; this greatly increases the the usefulness of the equipment by minimizing the amount of operator attention required, making more practical the simulation of very prolonged cooling treatments, and eliminating chances oferror.

BRIEF DESCRIPTION OF THE DRAWINGS A complete understanding of the invention may be obtained from the foregoing and following description thereof, taken together with the accompanying drawings, in which:

FIG. I is an elevational view, largely diagrammatic, illustrating a preferred arrangement of equipment in accordance with the present invention;

FIG. 2 is a plan view of a portion of the equipment shown in FIG. 1; and

FIG. 3 is an elevational view, largely diagrammatic, of equipment comprising an alternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As seen in FIGS. 1 and 2, a specimen or sample of metal M is held by holders 10 secured to the sides 12 ofa container 14, within which there is maintained a bed 16 of finely divided solids, such as silica sand or other suitable inert material, fluidized with combustion gas entering the chamber 14 from a plenum chamber 18 by means of a gas distribution plate 20 and suitable nonsifting caps 22. The chamber 14 is also provided with an overflow stand-pipe 24, for a purpose to be hereinafter more fully explained. Surrounding the chamber 14, there is suitable insulation 26.

The plenum chamber 18 contains a burner 28 of known type capable of using different quantities of excess air. The burner 28 is fed with air through line 30 and with gas through line 32. These lines may be provided with suitable valves and metering means (not shown).

The temperature of the metal M is sensed by means of a thermocouple 34, which may be clamped to or secured in the specimen of metal M in any of several known suitable ways. The thermocouple 34 has lead wires 36, which communicate with a controller 38.

The controller 38 is of a known type, mentioned above in the description of the prior art, e.g., a controller having a strip chart upon which there may be traced with a silver pencil a line corresponding to the changes desired in a particular parameter that is to be controlled, the controller having a probe for following the trace line as the strip chart is advanced at a steady rate and generating signals corresponding to the desired values of the parameter to be controlled. The controller 38 also receives signals from the thermocouple lead wires 36, corresponding to the actual temperature of the specimen or sample of metal M, comparing them with the signals corresponding to the position of the prove and generating a command signal, which is conveyed by the line 40 to the control 42 of a solids feeder 44. With the use of controller 38, cooling rates as high as 500 F. per minute can be achieved. The embodiment of FIGS. 1 and 2 is specifically intended for achieving relatively faster cooling rates such as about 50 to 500 F. per minute. It will be appreciated that when the specimen of metal M is to be cooled at a rate so rapid, there will be a substantial differential between the temperature of the solids in the bed 16 and the temperature of the metal M; thus, this is a factor to be taken into account in drawing the trace line on the strip chart if, for some reason, it is desired that the metal M be held serve a particular temperature after having been rapidly cooled from a higher temperature. In most instances, however, a steady cooling rate is desired, and the controller 38 acts to accelerate or decelerate the solids feeder 44 so as to maintain in the bed M a temperature differential adequate to achieve the desired rate of cooling. l have found that the mixing of the added solids in the bed I6 is quite rapid, so that the addition of cold solids and the concomitant overflow of mixed bed solids through the standpipe does serve as a convenient method for obtaining rapid changes in the total heat capacity of the fluidized bed system, and this provides a compact, efficient and automatic method for the controlled cooling of the samples of metal M.

The solids feeder 44 is preferably of a known type, as described above in the description of the prior art. It comprises a hopper 46, a housing 48, an adjustable gate 50 and an endless belt 52 driven by motor means (not shown) associated with the controller 42. Solids pass from the belt 52 to a discharge chute 54 and thence to the bed 16.

The apparatus described above is operated as follows. The metal M has its thermocouple 34 attached to it and is heated either in the bed or in separate equipment, not shown, to an appropriate austenitizing temperature such as about 1,600 F. An appropriate quantity of silica sand or the like is added to the container 14, e.g., enough to make it about half full. Then, flow of air and gas to the burner 28 is begun, and the burner 28 is ignited, to cause combustion gases to fluidize the solids to make the bed 16. An appropriate trace is drawn on the strip chart of the controller 38, and the strip chart is inserted into the controller 38. If the specimen M has been heated in the bed (which will in most cases prove most convenient), its temperature can be determined using the thermocouple 34, and when the specimen M has reached the desired starting tompersture, the controller 38 may be switched on. The solids feeder 44 will then also begin to operate. at an initial setting that is approximately correct to bring about the desired temperature change in the specimen M. It is within the skill of the art to calculate an appropriate setting, or one may be arrived at empirically. Smooth operation is achieved in a very short time.

If the specimen M has been heated in a separate furnace, the operation is similar. The specimen M is removed from the furnace, its thermocouple lead wires 36 are connected to the controller 38, and the controllers 38 and 42 are turned on as the specimen M is placed in the bed 16. Generally, this procedure will be used only where it is desired to have the specimen follow a time-temperature curve that begins with a rapid temperature change, usually a rapid cooling. This implies that the temperature of the bed 16 will be substantially different from that of the specimen M. A suitable difference to yield the desired change can be determined theoretically or empirically.

In any event, the operation is generally continued until the metal M is at about room temperature, at which time the burner 28 is turned off, as are the controller 38 and the solids feeder 44. The specimen of metal M is removed and may then be subjected to the usual tests, including a tensile test, an impact test, and a metallographic examination of the microstructure.

Referring now to FIG. 3, there is shown an alternative embodiment which is especially suitable for use when a slow cooling rate is desired. In FIG. 3, parts corresponding to those shown in FIGS. 1 and 2 are designated with like reference numerals. It will be seen that the apparatus of FIG. 3 is the same as that of FIG. 1, except that the solids feeder 44 is omitted and there is provided, in place of the insulation 26, a heating element 56 which surrounds the bed chamber 14. The heating element 56 contains means responsive to signals conveyed to it through line 58, coming from the controller 38, so that the temperature of the solids in the bed 16 may similarly be controlled.

Other modifications are possible. For example, the function of the controller 38 may be taken over by an operator, who reads on a suitable indicator the temperature signals carried by the leads 36 and then adjusts appropriately the setting of the controller 42 or the power supply of the heating element 56. Another possible modification is to supply equipment having both the solids feeder 44 and the heating element 56, appropriate switches being provided in the lines 40 and 58, so that a desired one of the modes of control, either that of FIGS. 1 and 2 or that of FIG. 3, may be used, in accordance with the cooling rate desired. Those skilled in the art will appreciate how the invention may be used to treat a specimen in a special atmosphere, such as hydrogen or argon gas.

While I have shown and described herein certain embodiments of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

lclaim:

1. Apparatus for cooling a piece of metal from an austenitizing temperature at a desired rate, said apparatus comprising, in combination,

a bed of suitable inert material,

means for fluidizing said bed with gaseous products of combustion,

means within said bed for sensing the temperature of said piece of metal and producing an output signal proportionate thereto,

a variable-speed means for feeding solids to said bed,

an overflow means in said bed for withdrawing mixed bed solids therefrom, and

means comprising a curve-following controller responsive to said signals for controlling the operation of said variable-speed means for feeding solids to said bed. 

